The fifth and sixth fields on each line are not used
by NFS, thus conventionally each contain the digit zero. For example:
.P
-.SP
-.NF
-.TA 2.5i +0.75i +0.75i +1.0i
+.nf
+.ta 8n +14n +14n +9n +20n
server:path /mountpoint fstype option,option,... 0 0
-.FI
+.fi
.P
The server's hostname and export pathname
are separated by a colon, while
.P
The
.I fstype
-field contains "nfs", for whatever version of the protocol.
-The
-.B nfs
-allow several mount options, which are described below.
+field contains "nfs". Use of the "nfs4" fstype in
+.I /etc/fstab
+is deprecated.
.SH "MOUNT OPTIONS"
Refer to
.BR mount (8)
option.
.TP 1.5i
.BI timeo= n
-The time (in tenths of a second) the NFS client waits for a
-response before it retries an NFS request. If this
-option is not specified, requests are retried every
-60 seconds for NFS over TCP.
-The NFS client does not perform any kind of timeout backoff
-for NFS over TCP.
+The time in deciseconds (tenths of a second) the NFS client waits for a
+response before it retries an NFS request.
+.IP
+For NFS over TCP the default
+.B timeo
+value is 600 (60 seconds).
+The NFS client performs linear backoff: After each retransmission the
+timeout is increased by
+.BR timeo
+up to the maximum of 600 seconds.
.IP
However, for NFS over UDP, the client uses an adaptive
algorithm to estimate an appropriate timeout value for frequently used
.IP
The DATA AND METADATA COHERENCE section contains a
detailed discussion of these trade-offs.
-.SS "Options for versions 2 and 3 only"
+.SS "Options for NFS versions 2 and 3 only"
Use these options, along with the options in the above subsection,
-for NFSv2/v3 only. They will be ignored for newer versions.
+for NFS versions 2 and 3 only.
.TP 1.5i
.BI proto= netid
The transport protocol name and protocol family the NFS client uses
.BI nfsvers= n
The NFS protocol version number used to contact the server's NFS service.
If the server does not support the requested version, the mount request fails.
-If this option is not specified, the client negociate a suitable version with
+If this option is not specified, the client negotiates a suitable version with
the server, trying version 4 first, version 3 second, and version 2 last.
.TP 1.5i
.BI vers= n
is specified, the client assumes that POSIX locks are local and uses NLM
sideband protocol to lock files when flock locks are used.
.IP
-To support legacy flock behavior similar to that of NFS clients < 2.6.12, use
-'local_lock=flock'. This option is required when exporting NFS mounts via
+To support legacy flock behavior similar to that of NFS clients < 2.6.12,
+use 'local_lock=flock'. This option is required when exporting NFS mounts via
Samba as Samba maps Windows share mode locks as flock. Since NFS clients >
2.6.12 implement flock by emulating POSIX locks, this will result in
conflicting locks.
.IP
NOTE: When used together, the 'local_lock' mount option will be overridden
by 'nolock'/'lock' mount option.
-.SS "Options for version 4 only"
+.SS "Options for NFS version 4 only"
Use these options, along with the options in the first subsection above,
-for NFSv4 only. They will be ignored with older versions.
+for NFS version 4 and newer.
.TP 1.5i
.BI proto= netid
The transport protocol name and protocol family the NFS client uses
file causes the mount command to negotiate
reasonable defaults for NFS behavior.
.P
-.NF
-.TA 2.5i +0.7i +0.7i +.7i
+.nf
+.ta 8n +16n +6n +6n +30n
server:/export /mnt nfs defaults 0 0
-.FI
+.fi
.P
Here is an example from an /etc/fstab file for an NFS version 2 mount over UDP.
.P
-.NF
-.TA 2.5i +0.7i +0.7i +.7i
+.nf
+.ta 8n +16n +6n +6n +30n
server:/export /mnt nfs nfsvers=2,proto=udp 0 0
-.FI
+.fi
.P
Try this example to mount using NFS version 4 over TCP
with Kerberos 5 mutual authentication.
.P
-.NF
-.TA 2.5i +0.7i +0.7i +.7i
+.nf
+.ta 8n +16n +6n +6n +30n
server:/export /mnt nfs4 sec=krb5 0 0
-.FI
+.fi
.P
This example can be used to mount /usr over NFS.
.P
-.NF
-.TA 2.5i +0.7i +0.7i +.7i
+.nf
+.ta 8n +16n +6n +6n +30n
server:/export /usr nfs ro,nolock,nocto,actimeo=3600 0 0
-.FI
+.fi
.P
This example shows how to mount an NFS server
using a raw IPv6 link-local address.
.P
-.NF
-.TA 2.5i +0.7i +0.7i +.7i
+.nf
+.ta 8n +40n +5n +4n +9n
[fe80::215:c5ff:fb3e:e2b1%eth0]:/export /mnt nfs defaults 0 0
-.FI
+.fi
.SH "TRANSPORT METHODS"
NFS clients send requests to NFS servers via
Remote Procedure Calls, or
NFS version 4 ACLs are not fully compatible with POSIX ACLs; as such,
some translation between the two is required
in an environment that mixes POSIX ACLs and NFS version 4.
-.SH FILES
-.TP 1.5i
-.I /etc/fstab
-file system table
-.SH BUGS
-The generic
-.B remount
-option is not fully supported.
-Generic options, such as
-.BR rw " and " ro
-can be modified using the
-.B remount
-option,
-but NFS-specific options are not all supported.
+.SH "THE REMOUNT OPTION"
+Generic mount options such as
+.BR rw " and " sync
+can be modified on NFS mount points using the
+.BR remount
+option.
+See
+.BR mount (8)
+for more information on generic mount options.
+.P
+With few exceptions, NFS-specific options
+are not able to be modified during a remount.
The underlying transport or NFS version
cannot be changed by a remount, for example.
+.P
Performing a remount on an NFS file system mounted with the
.B noac
option may have unintended consequences.
The
.B noac
-option is a mixture of a generic option,
+option is a combination of the generic option
.BR sync ,
-and an NFS-specific option
+and the NFS-specific option
.BR actimeo=0 .
+.SS "Unmounting after a remount"
+For mount points that use NFS versions 2 or 3, the NFS umount subcommand
+depends on knowing the original set of mount options used to perform the
+MNT operation.
+These options are stored on disk by the NFS mount subcommand,
+and can be erased by a remount.
.P
+To ensure that the saved mount options are not erased during a remount,
+specify either the local mount directory, or the server hostname and
+export pathname, but not both, during a remount. For example,
+.P
+.NF
+.TA 2.5i
+ mount -o remount,ro /mnt
+.FI
+.P
+merges the mount option
+.B ro
+with the mount options already saved on disk for the NFS server mounted at /mnt.
+.SH FILES
+.TP 1.5i
+.I /etc/fstab
+file system table
+.SH BUGS
Before 2.4.7, the Linux NFS client did not support NFS over TCP.
.P
Before 2.4.20, the Linux NFS client used a heuristic